Method of and apparatus for electrically determining the formation in wells



012mm KUUM March 26, 1946. H, Ewuls' METHOD OF AND APPARATUS FOR ELECTRICALLY "DETERMINING THE FORMATION IN WELLS Filed Aug. 4, 1936 4 Sheets-Sheet 1" [A/ v/v TOR GEORGE H. [NA/l6 A 770R NE).

March-26, 1946. G H ENNIS IARC ROON 2,397,255 METHOD OF AND APPARATUS FOR ELEcTRIcALLY DETERMINING THE FORMATION IN WELLS Filed Aug. 4, 1956 A Sheets-Sheet 2 Arroezvzx MKUH ROOM March 26, 1946. G. H. ENNIS 2,397,255

METHOD OF AND APPARATUS FOR ELECTRICALLY DETERMINING THE FORMATION IN WELLS Filed Aug. 4, 1936 4 Sheets-Sheet 3 [/v VENTOR GEORGE h. E/v/v/s March 26, 1946. e. H. ENNIS METHOD OF AND APPARATUS FOR ELECTRICALLY DETERMINING THE FORMATION IN WELLS 4 Sheets-Sheet 4 Filed Aug. 4, 1936 ATToR/vL-x htARfiH RGGN? UNITED STATES PATENT OEFKE METHOD OF AND APPARATUS FOR ELEC- TRICALLY DETERMINING THE FORMA- TION IN WELLS George Henry Ennis, Long Beach, Calif., assignor of one-half to Robert V. Funk, Long Beach,

Calif.

Application August 4, 1936, Serial No. 94,174

25 Claims.

My invention relates to the art of determining the location of subterranean strata, and relates particularly to a method of and apparatus for determining the character of various strata and their location, and also for determining the nature of the fluid content of such strata.

In describing and illustrating the various features, advantages, and objects of my invention I will refer to its use in the oil producing industry where it is of considerable value and utility. My invention, however, may be used in other industries wherein there exists a bore hole in which it is desired to locate the various strata and determine their fluid content. I believe my invention to be new not only in its entirety but in its several subcombinations and elements and in the various steps of the process which I have invented. I therefore desire patent protection not only upon the method and apparatus as a whole but on the several elements, parts, steps, or subcombinations thereof which compose the whole.

Referring to the oil producing industry, in practically every oil field there are numerous layers of oil sands or oil bearing formations separated by layers of shale or rock and also separated by water sands. The most productive high pressure oil bearing formations are usually below the more shallow sands, and in order to obtain maximum production it is the usual practice to drill through the more shallow oil sands to the high pressure formations. In order to shut off all of the other formations above the one which is being produced, a well casing is installed in the well, this Well casing having a shoe on the lower end which is cemented to a shale or rock formation usually found immediately above the formation being produced.

When the high pressure oil bearing formation becomes depleted, it is the present practice to cement off the depleted formation and to perforate the casing at a, point opposite of the more shallow oil sands to obtain whatever oil is present in such more shallow oil sands. If an accurate log of the well has been kept, the position of these more shallow oil bearing formations is known and perforation at the proper level can be performed. If a log has not been kept, it is then necessary to locate the more shallow oil bearing formations.

It is an object of my invention to provide a method and apparatus which may be used on wells, in which the well casing has been installed,

for determining the locations of the strata between the lower end of the casing and the surface of the ground. By use of my invention it is possible to obtain information by which the location of the various shales and Sands may be determined, and with this information it is possible to perforate the well casing at such a point that the oil sands will be communicated with the well and thus put on production.

It is an object of my invention to provide an electrical method by which the various strata can be located notwithstanding the presence of the well casing in the well.

It is a further object of my invention to provide a method and apparatus which do not involve mathematical computations or calculations to obtain or use the information which is given by the use of my invention.

It is a still further object of my invention to provide a method and apparatus in which the apparatus during the performance of the method produces a chart which of itself and without mathematical computations or calculations shows the locations of various sands, shales, and other formations.

In my copending application entitled Method and apparatus for electrically coring in cased bore holes, Serial No. 28,891, filed June 28, 1935, I have described and disclosed a method and apparatus in which the strata may be located in cased bore holes, which method has been put into commercial use and has proven to be highly satisfactory and of great commercial value. In the performance of my method on certain wells it is found that the curves produced by the apparatus, and which indicate the location of the various strata, are not as sharp and distinct as on other wells. Upon investigation it has been found that this usually results from the presence of a sandy shale formation or a shaly sand formation or unusual conditions which produce a curved portion in an intermediate position on the graph produced. Thus, sandy shale indications or shaly sand indications are sometimes hard to distinguish from sand formations having water therein, and therefore in performing the method of my invention and in using the apparatus of my invention on such wells it is necessary to be particularly attentive and careful in performing the process.

It is an object of my present invention to provide an improved method and apparatus which may be used on all wells but which is particularly useful on what I term the more difiicult wells, and which produces relatively sharp and distinct curves so that the various formations which were previously difiicult to locate may be very easily located in the present invention.

It is another object of my invention to provide a method and apparatus in which extraneous disturbances, such as interfering earth currents or electrical phenomena from generators, motors, power lines, etc., are eliminated.

It is an object of my invention to provide a method and apparatus in which the direction of flows of current or polarity is reversed on the formation being tested.

In certainwells which have been tested it is difficult to determine the fluid content of the strata which have been located. The readings indicating sandy shales or shaly sands sometimes approximate the readings indicating sand having a water content. It is therefore an object of my present invention to provide a method and apparatus which not only locate the strata and indicate the structure of the strata, but also indicate the fluid content, if any, of the strata.

It is a still further object of my invention to determine the reaction of direct current electrical characteristics and alternating current electrical characteristics on the formations in a well, and in this manner determine the structure thereof, as well as the fluid content thereof.

It is a still further object of my invention to determine the reaction on direct current electrical characteristics and alternating current electrical characteristics of the formations in a well, and in this manner determine the structure thereof, as well as the fluid content thereof.

It is a still further object of my invention to provide a method and apparatus in which the direct current electrical characteristics provide a path for the alternating current electrical characteristics in order that the influence or effect of the various strata in the well on the alternating current electrical characteristics may be determined.

It is sometimes desirable to locate the various formations before the casing is installed in the well; and my invention in certain embodiments is adapted for such use.

My invention is susceptible of embodiment in many different forms, all of which incorporate the essential features of my invention. It is found in practice that certain wells may employ a slightly different set-up of apparatus. In the following description I will describe a preferred form of my invention which includes all of the features and advantages thereof in their entirety, and I will also describe other forms which include certain features of my invention, but which have a more limited utility in the industry. It should be understood, however, that I do not wish to be limited to the apparatus which I have chosen to illustrate the different embodiments of my invention.

Referring to the drawings in detail:

Fig. 1 is a diagrammatic view illustrating a preferred form of apparatus which performs the preferred method of my invention.

Fig. 2 is a view similar to Fig. 1 but showing parts of the apparatus in different positions which are assumed during the performance of my method and during the operation of the apparatus.

Fig. 3 is a view showing a record or chart which was made with the apparatus corresponding to that diagrammatically illustrated in Figs. 1 and 2.

Fig. 4. is a diagrammatic view illustrating an alternative form of my invention in which the reversing means has been eliminated.

ascmts Fig. 5 is a view illustrating an alternative form of my invention which employs but a single direct current circuit or ionic flow which sets up a path for the alternating current or alternating current potential.

Referring to the drawings in detail, and particularly Figs. 1 and 2, the numeral ll represents a Well which has been drilled to an oil bearing formation I 2. Installed in the well is a well casing I4, the lower end of which has been cemented to a layer of shale l6 in order to seal from the well all of the formations above the oil bearing formation l2. The oil bearing formation 12, it will be assumed, has ceased to profitably yield, but it is desired to locate oil bearing formations at a higher point so that the well casing 14 can be perforated and the other oil bearing formations put on production. For this purpose apparatus built in accordance with my invention is installed as follows: Connected to the well casing M, as indicated at I9, is a well casing conductor IS, The well casing conductor It extends to a commutator 2B which constitutes a meter reversing means. The commutator 20 has movable contacts 2! and 22 supported out of electrical contact with each other and adapted to be rotated by a shaft 23 connected to a rotating means 24. The commutator 2!] includes four stationary contacts 26, 21, 28, and 29. The well casing conductor i8 is connected to the stationary contact 26. Connected to the stationary contact 21 is a conductor 30 which extends to a recording meter 3| which may record milliamperes or millivolts, and which is preferably of the construction indicated by the numeral 3! and shown in Fig. 2 of my copending application referred to heretofore. Extending from the meter 3! is a conductor 33 which is connected to the stationary contact 29. Connected to the stationary contact 28 is a conductor 34 which extends to a ground reversing means or commutator 36 which includes movable contacts 3'! and 38 adapted to be rotated by a shaft 39 preferably connected to the commutator 20; and also includes stationary contacts 4|, 42, 43, and M. The conductor 34 is connected to the stationary contact M.

The commutator 36 is adapted to alternately connect the well casing I l with one of two grounds 46 or 41, which are preferably installed in the earth a distance from each other and a distance from the well, as will be pointed out after the various circuits have been described. Connected to the ground 46 is a conductor 48 which extends to the commutator 36 and is connected to the stationary contact 42. With the commutators 36 and 26 in the positions shown in Fig. 1, the meter Si is connected in one direction in the circuit, and the ground i6 is in circuit with the well casing conductor l8 and the well casing l4. Connected to the ground 41 is a conductor 50 which extends to the commutator 36 and which is connected to the stationary contact 43 thereof. When the commutator has been rotated into the position shown in Fig. 2, the ground 46 and its conductor 48 are disconnected from the well casing, and the ground 41 and its conductor 50 are connected to the well casing.

For the purpose of balancing the recording meter 3| there are provided a battery 53 and an adjustable rheostat 54 which are included in a shunt circuit 55 which is connected on opposite sides of the recording meter 3|.

Adapted to be extended into the well I I is a well conductor 58 which is wound on a drum 59 and extends therefrom over a sheave 60 and into the well. The lower end of the well conductor 58 has an electrode 6| secured thereto which preferably includes means in the form of arms 62 for holding it in a concentric position in the well. The well conductor 58 extends from the drum 59 to the stationary contact 44 of the commutator 36 and has a recording meter 63 which may record milliamperes or millivolts of this conductor. The conductor may also include a battery 64 and adjustable rheostat 65 for providing electrical characteristics in the well conductor 58 or for controlling the magnitude thereof.

It will be seen that when the commutator 36 is in the position shown in Fig. 1 the casing conductor I8 is connected to the ground 46, and that when the commutator is in the position shown in Fig. 2 the well conductor 58 is connected to the ground 46.

Connected to the well conductor 58 at a point 10 is an alternating current conductor H, the opposite end of which is preferably connected at a 'point 12 in electrical communication with the ground 41. Associated with the alternating current conductor 11 is a source of alternating current 13 and an alternating current meter 14 adapted to record either the amperage or voltage of this conductor. To prevent alternating current from flowing through the conductor 56 to the commutator 36 there is provided an alternating current choke 15.

As stated heretofore, the meter 3! is preferably of the construction illustrated in Fig. 2 of my copending application and is connected to a flexible cable 11 to a sheave 18 which is engaged by the well conductor 58 and is rotated thereby in order to operate the meter 3!. The meter 14 may also operate on this same principle and may therefore have a flexible cable 19 which may also be connected to the sheave l8 and operated thereby.

In performing the method of my invention illustrated in Figs. 1 and 2, the apparatus is first installed as illustrated in Figs. 1 and 2. In my invention I depend upon electrical characteristics set up in two circuits which I provide and which I call an external well circuit and an external casing circuit. The external well circuit includes the electrode 6!, the well conductor 53, and, with the parts in the positions shown in Fig. 1, the conductor 50 and ground 41. parts in the positions as shown in Fig. 2, the well circuit includes the conductor 43 and the ground 46 in place of the conductor 50 and ground 41. The casing circuit, with the parts in the positions shown in Fig. 1, includes the well casing conductor l8, the conductor 34, and the electrical connections between these two conductors including various conductors and the meter 3| and the conductor 48 and ground 46. However, with the parts in the positions shown in Fig. 2, the casing circuit includes the conductor 56 and ground 41 rather than the conductor 48 and ground 46. The external alternating current circuit of my invention includes the ground 41, the alternating current conductor 1|, the well conductor 58, and the electrode Bl.

In the utilization of my invention I prefer to employ the galvanic properties of the earth, and it is therefore desirable to provide the electrode 6| and the grounds 46 and 41 from suitable electro-potential materials. Since the well casing I4 is made from iron, it is necessary to select grounds 46 and 41 of suitable electro-potential values relative to the casing. In the preferred form of my invention the electrode 61 is prefer- However, with the l ably electro-positive with respect to the iron casing [4 and is ordinarily made from zinc. It is furthermore desirable that the ground 41 be electro-negative with respect to the iron casing l4, and I prefer to make this ground from copper or I may use nickel, lead, silver, antimony, gold, etc. In order to establish a voltaic cell between the electrode BI and the well casing l4 an electrolyte, such as indicated at 80, is employed in the well. This electrolyte may be the natural water in the well or may be one which has been mixed or prepared at the surface of the ground and deposited in the well. The ionic flow in the voltaic cell provided by the electrode 6| and casing I4 is from the electrode 6| to the casing [4. The casing 14 and the ground 41 in the preferred form of my invention also act in conjunction with the intervening earth as a voltaic cell, and the flow of current is from the casing M to the ground 41 as indicated by the arrows 8!.

It is desirable that the ground 46 be electropositive with respect to the iron casing i4, and I therefore prefer to make the ground 46 out of zinc so that the ionic flow will be from the ground 46 to the casing 14 as indicated by arrows 82. It will be seen from Fig. 1 that the internal flows of current are complementary to the external flows of current or, in other words, the internal circuits are complementary to the two external circuits which I provide. In using the apparatus I prefer to direct the flow of current through the external circuits in a manner to employ and act with the current flows generated in the earth.

If the flow of current or the potential in either of the circuits is not satisfactory, battery means or other source of energy or potential may be inserted in either one or both of the circuits such, for example, as the battery 64 in the conductor 58 which has the rheostat 65. Where the current or potential produced by the galvanic action in the earth is adequate, this battery and rheostat are unnecessary and need not be used. If the current flow is too great, a battery opposing the current flow may be used, or if it is insufficient, a battery connected to increase the flow or increase the potential may be used. This is true with respect to either of the circuits shown.

The apparatus illustrated in Figs. 1 and 2 has been used for testing a well, and I will refer, in describing the method of my invention and the operation of the apparatus, to actual positioning of parts and voltages and amperes used in the test which is the same as that disclosed in my copending application, supra. The ground 41 was located approximately feet from the well I I and the ground 46 was located at approximately 125 feet from the ground 41 and approximately 250 feet from the well II. The two grounds 46 and 41 were situated at such points as to have but a minimum of electrical interference in the circuits, and this positioning is followed out in practice even though it is necessary to locate the grounds closer together, farther apart, or closer to, or farther from the well. It is found highly desirable to keep the grounds, if possible, away from surface piping which forms conductors, which ultimately lead to the well being tested. After the apparatus has been installed as illustrated, the electrode BI is lowered into the well. It is possible, by connection of meters to and in series with the various external conductors, to determine the potential differences between the various parts in the ground. In the test being described the millivolts between the electrode 6| and casing [4 were 200 and the milliamperes 6, the electrode 6| being internal positive with respect to the casing l4. The'mlllivolts between the electrode 6| and the ground 41 were 800 and the milliamperes 9, the ground 41 being internal negative. The millivolts cet-ween the electrode 6| and the ground 46 were 325 and the milliamperes 2.5, with fresh water as an electrolyte 80, the ground 46 being internal positive, or if the electrolyte 80 is salt water or mud or any strongly electrolytic material, the ground being internal negative. The millivolts between the casing l4 and the ground 41 were 525 and the milliamperes were 15.5, the ground 41 being internal negative. The millivolts between the casing l4 and the ground 46 were 600* and the milliamperes were 11, the casing l4 being internal negative. The millivolts between the ground 41 and the ground 46 were 1050 and the milliamperes were 18.5, and the ground 46 was internal positive.

If the voltages and amperes are not suitable to obtain a satisfactory test, they may be increased or decreased, as pointed out heretofore, by the use of batteries. However, it should be understood that under ordinary circumstances batteries are unnecessary. It should further be understood that the flow of current or potential set-u in the well circuit can be increased or decreased by changing the strength of the electrolyte 80 which is used in the well.

After the parts have been arranged as shown and the voltages and ampere flows established, it is then desirable to balance the meter 3|, that is, to adjust the rheostat 54 to bring the indicating needle of the meter into a central position so that when it fluctuates in response to electrical characteristics in the circuit it will not move off of the scale. After this is done the apparatus is ready for making the test and recording the information, by means of which the strata may be located.

The commutators 20 and 36 are set into operation by an energization of the rotating means 24. I prefer to rotate the commutators to reverse the circuits approximately 500 times per minute, but diiferent rates of rotation may be employed. The position of the electrode 6| is known since the conductor 58 has been measured, and during the making of the test this electrode 6| is gradually raised in the well. Due to the fact that the meter 3| is associated with the conductor 58 the chart which is formed will indicate the level at which the various electrical phenomena occurred. In taking the readings the same mode of procedure is followed as outlined in my copending application referred to and employing the apparatus illustrated in Fig. 2 of that application.

It will be understood that during the making of the test the commutators 20 and 36 are being rotated and that the conductors l8 and 58 are alternately connected to the two grounds 46 and 41, and that the meter 3| in reality records the average millivolts or milliamperes which flow through the casing circuit when connected either to one ground or the other.

When the parts are in the positions shown in Fig. 1, there is a flow of current through the conductor 50 from the ground 41 to the stationary contact 43 through the movable contact 38 and to the stationary contact 44 of the commutator 36. From there it flows through the conductor 58 to the electrode 6|. The current likewise flows from the electrode 6| through the electrolyte 80 to the well casing I4, and it is assumed that to complete this circuit there is a flow of current through the earth from the well casing l4 at a point adjacent the electrode 6| to the ground 41. This flow of current in the external circuit or the well circuit, which is in effect with the parts in the positions shown in Fig. 1, is in a direction indicated by the arrows 96. At this same time there is a flow of current through the conductor I8 from the top of the casing l4 to the ground 46. This current flows to the stationary contact 26, movable contact 2|, and the stationary contact 21 of the commutator 26, to the conductor 3|] through the meter 3| and conductor 33 to the stationary contact 29, the movable contact 22, and the stationary contact 28 of the commutator 2|]. The current flows from the stationary contact 28 through the conductor 34 to the stationary contact 4|, the movable contact 31, and stationary contact 42 of the commutator 36. The current then flows from this stationary contact 42 through the conductor 46 to the ground 46. In order to complete this external circuit which is referred to as the casing circuit, it must be assumed that there is an internal flow of current from the ground 46 to the casing 4 as indicated by arrows 82. The flowof currrent through the external casing circuit, with the parts in the positions shown in Fig. 1, is indicated by arrows 9|.

When the commutators are in opposite positions, as shown in Fig. 2, the flows of current are as follows: The grounds 4'6 and 4'! have been reversed, and therefore the flows of current through the well circuit and through the casing circuit are reversed. It is substantially the same effect as placing in the circuits batteries or voltaic cells of opposite potentials which would cause flows of current or voltages in opposite directions. With the parts in the positions hown in Fig. 2, the flow of current in the casing circuit which now includes the ground 4? rather than the ground 46 is upward through the conductor 50 to the stationary contact 43, through the movable contact 31, and to the stationary contact 4| of the commutator 36. The current flows from the stationary contact 4| through the conductor 34 to the stationary contact 28, the movable con tact 22, and the stationary contact 2'! 0f the commutator 26. The current then flows from the stationary contact 21 through the conductor 3|], the meter 3|, the conduct-or 33, the stationary contact 29, the movable contact 2|, and the stationary contact 26 of the commutator 26 to the well conductor |8, through which it flows to the upper end of the casing l4. This flow is referred to by arrows bearing the numeral 93 which is complementary to and in the same direction as the flow of current from the well casing M to the ground 41, as indicated by the arrows 8|. It will be noted that the commutator 2|] reverses connections in the conductors in such a way that the direction of flow of current into the meter 3| is always in the same direction.

With the parts in the positions shown in Fig. 2, the flow of current through the well circuit is upwardly through the conductor 58, to the stationary contact 44, the movable contact 38, and the stationary contact 42 of the commutator 36, from whence the current flows through the conductor 48 to the ground 46. It will be seen that at this time the flow of current in the Well circuit is complementary to the flow of current between the ground 46 and the Casing I4, as indicated by the arrows -82. The flow of current in the well circuit is indicated by arrows 94.

It will be seen that the flows of current in the casing circuit and in the well circuit are opposed to each other, and this is preferable in my invention. If the flow of current in the well circuit is not sufficiently strong, it may be increased by operating the rheostat 65, or if it is too strong it may be reduced by an opposite operation of this rheostat. It is found that the flow of current or the potentials in one circuit has a direct effect upon the flow of current or potentials in the other circuit, and that by striking a proper balance such as given heretofore better readings may be obtained.

Before discussing the flow of current in the alternating current circuit I will describe the operation of the apparatus involving direct current flows and will thereafter describe the operation of the apparatus involving alternating current flows.

When the electrode BI is in different positions in the well, the electrical characteristics (which term I use to broadly identify either voltage. amperage, or both) in both the conductors I8 and 58 change, and there is a definite cause and effect relationship between the current flows and voltages in these two conductors. It appears that whenever the electrode BI is opposite a shale, for example, there are certain electrical characteris tics set up in the conductors l8 and 58, and that when the electrode 6! is opposite a sand, for example, there are certain other electrical characteristics set up in the conductors l8 and 58. Experience has indicated that in a certain location a given electrical characteristic accurately indicates certain data in connection with the stratum or formation (as will be pointed out in detail when reference is made to Fig. 3 which shows a graph made from a well in the test under discussion) which is directly adjacent the electrode 6|, and this holds true with such accuracy that it is possible to obtain a record as shown in Fig. 3 which can be used by geologists to locate various formations and to find the level at which the casing M should be perforated in order to obtain oil.

I am not absolutely certain as to the theory on which my invention operates, and I therefore prefer to describe exactly what I do in order that I may comply with the patent statutes in teaching the art how to practice my invention, and I believe it to be immaterial as to the theory on which my invention operates so long as it operates and so long as I instruct those skilled in the art how to obtain the novel results of, my invention. However, without desiring to be limited to any theory of operation which may prove to be erroneous in certain respects, I believe that the stratum adjacent the electrode 6| influences the current or voltage because of resistance of the particular formation. It is, of course, well known that batteries or voltaic cells have internal resistance. In the ground I believe that the casing I4 acts as one plate, while the grounds 46 and 41 act as other plates, and the earth and its fluid act as an electrolyte of a battery. The point at which the electricity flow or voltage passes to or at which voltage is impressed on the casing M and the adjacent strata is determined by the position of the electrode 6!, and in this manner changes in electrical characteristics in the external circuits are directly influenced or controlled by the formation immediately adjacent the electrode I.

It is possible to obtain a reading and to met a curve either from the current characteristics in the casing circuit or the well circuit, and these MIR curves are very reliable. In the form of my invention shown herein, the recording meter 3| is placed. in the casing circuit l8 but may. if desired, be placed in the well circuit 58.

In the performance of the invention, as stated heretofore, the electrode BI is elevated to different known positions in the well, and the indications on the recording meter are observed and a curve drawn in accordance therewith.

As stated heretofore, certain wells penetrate certain peculiar formations, such as sandy shales or shaly sands, and the curves indicating such formations are difficult to distinguish from sand formations including water. I have discovered that alternating current, when passed through the formation in the same manner as a direct current is passed through the formation, will more distinctly indicate the structural characteristics of the formation and may be used alone or in conjunction with the direct current reading. Since the direct current readings indicate, at least in part, the fluid contents of the formation, and the alternating current indicates the structure of the formation, I am able to combine the two readings to determine the structure of the formation and the fluid contained therein. At any rate the two readings when taken together have been foundin practice to be highly reliable. As shown in Figs. 1 and 2, the alternating current conductor H is at all times connected to the well conductor 58 and to the ground 41. The flow of alternating current is therefore in opposite directions in the external Well circuit, as indicated by the double headed arrows 96. This flow of alternating current is produced by the source of alternating current I3 and it may be of different values. It may range from a relatively low voltage up to a relatively high voltage and the amperage may also change. The voltage and amperage employed depend somewhat upon the apparatus available, and in the apparatus used in the test under discussion the voltage employed was 5 volts and the amperage was 50 to milliamperes. It is likewise possible to employ various frequencies. I prefer. however, to use 60 cycles per second, since a 60 cycle apparatus is readily available for use. The current flowing through this external circuit is indicated by the alternating current meter 14.

It must be assumed that for current to flow through the external circuit this circuit must be completed within the earth, and that the alternating current flows from the electrode 6| through the earth to the ground 41, as indicated by the double headed arrows 91. In the performance of my invention the flow of direct current indicated by the arrows 8| forms a path which is followed by the alternating current.

The alternating current enters the formation at a point in the well opposite the electrode 6|. Therefore, the electrical characteristics of the alternating current are directly affected or controlled by thi formation. The electrical characteristics are recorded on the alternating current meter 14 and a chart or curve may be plotted directly, as in the case of the direct current readings taken on the meter 3 l In Fig. 3 I have shown two curves, the one on the right being the direct current curve, and the one on the left being the alternating current curve, these curves being made directly on the meters 3| and 14, respectively.

Referring to Figs. 3, and first to the direct current curve, all peaks to the left, such as shown at I00, indicate shales, and all peaks to the right,

KUUM

such as IUI, indicate sands. Where the peaks are very pronounced, as at I02, I03, and H10, this is an indication of sands containing fluid and usually containing oil. Where the peaks to the right are less prominent, such as at I05 and I00, it is an indication of sands which contain water. Referring to the alternating current curve, the peaks to the left, such as represented by the numeral I08, represent shale, and the eaks to the right, such as indicated at I09, indicate sand formations. Since the alternating current appears to be more susceptible to formations of sandy shale and shaly sand, we find such formations indicated on the alternating current curve with much better definition than they are indicated on the direct current curve. For example, see the intermediate peaks indicated at III], I II, and H2. Formations containing water are also very distinctly indicated on the a1ternating current curve as indicated at IHI. In using the two curves in conjunction with each other, wherever both of the curves indicate prominently a sand such, for example, as at I 5 on the direct current curve and I I6 on the alternating current curve, there is an oil bearin formation. Iowever, where the direct current curve indicates a slight presence of oil, such as at H'I, while the alternating current curve indicates water as at I I8, this in an indication that the sands are water bearing sands. It is believed that where the sands originally contained oil and water has crept in, and where the sand has not been completely washed free of the oil, that in the direct current curve there is an indication of a slight amount of oil. However, this small amount of oil in the form of filament surrounding sand particles does not seem to affect the alternating current curve, hence we get the indication of the presence of water, as indicated at H8.

It should be understood that these curves are of value in locating oil bearing formations, shales, and water bearing formations when used in conjunction with data already accumulated. In the fields in which numerous tests have been made on wells in which the positions of the various strata are known, curves are obtained and these curves are studied so that in particular fields and particular locations the meaning of different amplitudes and shapes or curves can be established. Then when a test is made in a well in which the conditions are unknown and curves are obtained, these curves can be compared with the curves obtained where the conditions are known, and as a result of such comparison it is possible for the geologist to locate where the oil bearing formations are, where the shales are, and where the water bearing formations are. It is possible on many wells to use either the direct current curve or the alternating current curve. However, in some instances where peculiar conditions exist, it is highly desirable to employ both curves so that a more reliable and distinct indication can be obtained. The test which is represented by the chart of Fig. 3 represents the test made in a well where there are many small formations present, many formations composed of shaly sands, and sandy shales. By use of the two curves it was possible to definitely locate sands where oil was present such, for example, as indicated at I04 and H6. It will be noted that this body of sand is situated between two shales, and that these two shales exclude water which may exist above the upper shale and below the lower shale. By this test it has been determined that a good oil bearing sand is located at 3320 to 3335 feet below the surface of the ground. The chart or curves of Fig. 3 also indicate the presence of other oil bearing formations, but the formation at 3320 to 3335 feet appears to be the best formation. A very good oil bearing formation is also indicated by the peaks I20 of the direct current curve and I2I of the alternating current curve at a level of 3750 feet to 3770 feet.

The form of my invention both in apparatus and in method described heretofore is the preferred form of my invention which I find to be most satisfactory on all wells. It should be understood, however, that various modifications may be made and certain parts may be eliminated and other parts employed. I believe, however, that if any elements or steps of the process thus described are eliminated, the most satisfactory results cannot be obtained at all times. However. as explained heretofore, in certain wells two curves are not necessary to obtain satisfactory results.

In Fig. 4 I have illustrated a form of my invention which does not employ the circuit reversing means and meter reversing means in the form of the commutators 36 and 20. In this form of my invention the casing circuit is always connected to the ground 36 and the well circuit is always connected to the ground 67. In this form of my invention the readings taken on the meter M are the conditions which exist in the conductor I8 when connected to the ground 46 rather than the combination of the conditions existing in the conductor I8 when alternately connected to the grounds it and 41, as in Fig. 1. In this form of the invention, however, both the direct current curve and the alternating curve may be plotted to obtain the necessary geological information.

In the form of my invention shown in Fig. 5 I have eliminated completely a casing circuit. Two flows of current or two potentials are established between the electrode BI and the ground II. The direct current flow or direct current potential sets up a path, as indicated by the arrows M, which path is followed by the alternating current flow or the alternating current potential indicated by the arrows 9?. In this form of my invention the test may be made in a well with or without a casing.

It is believed that the forms of my invention illustrated herein and the processes described are sufiicient to teach those skilled in the art how to perform my invention and to indicate the scope thereof. I readily appreciate that various modifications and alterations may be made in the apparatus and the method of my invention without departing from the spirit and scope thereof. However, as I am at present advised, I believe that if any of the features or steps are eliminated, the valuable results of those steps will be sacrificed. Although results may be obtained, they will not be as wholly successful and as uniformly dependable as where the preferred form of my invention is used.

The indicator or recorder which I prefer to use in the practice of my invention is a millivoltmeter which measures the voltages and changes in voltages which occur when the electrode BI is moved into different positions in the well. However, amperes, current flow, resistance, or other electrical values may be measured. Likewise, the electrical values of these different types which are produced in the external circuits may be produced as a result of or may be affected by the current flow, voltage, resistance, impedance, condenser effect, etc. in the formation along side of the electrode 6| or the formations adjacent thereto. Obviously, my invention is not limited to the indicating, recording, or measuring of any particular type of electrical value which is produced during the performance of the method of my invention, and therefore I employ the term electrical characteristics as inclusive of these different electrical values which exist or may be measured. The term electrical characteristics therefore is intended to mean the voltage, amperage, resistance, impedance, condenser values, or other electrical phenomena which may be measured, indicated, recorded, or determined in order to obtain information whereby a curve, such as shown in Fig. 3, may be developed.

As has been fully pointed out in the course of the preceding detailed description of my invention, there are changes which occur in the electrical characteristics or electrical values in the external conductors or in the external circuits, which changes are produced when the movable electrode 6| is moved into different elevational positions in the well. In order that these different electrical characteristics or electrical values may be compared, such as by the makin of a chart as shown in Fig. 3, it is necessary to determine or find out what these electrical changes are. For this purpose it is convenient to use a meter, such as the meter 3|, 6|, or M, which is operable in response to the electrical characteristics which exist in any of the conductors, and the action of which changes as the electrical characteristics change. This operation is commonly referred to as measuring, and the meters therefor may be referred to as a means for measuring electrical characteristics. Likewise, the step by means of which the changes in electrical characteristics in the external circuits are made intelligible or available for use may be referred to as the step of measuring. In the use of these terms it should be understood, however, that the terms are used in their broad sense and cover indicating, recording, determining, or other ways of obtaining for use the information desired.

By the term alternating current electrical characteristics I refer to alternating current flows, alternating potentials, or capacity, frequency, or impedance, or other alternating current phenomena or effects.

I claim as my invention:

1. A method of determining the location of strata in a well having a well casing installed therein which includes the steps'of: forming an external circuit between said casing and the earth; forming an external circuit between an electrode in said Well and the earth; reversing the electrical pressure in at least one of said external electrical circuits; moving said electrode in said well; and measuring the electrical changes in at least one of said external circuits for different positions of said electrode.

2. A method of determining the location of strata in a well in which a well casing has already been installed, the steps of forming an external circuit between the casing and the earth; forming a second external circuit from an electrode in said well to the earth; reversing the connections of said external circuits to the earth; changing the position of said electrode in said well; and measuring the change of electrical characteristic in at least one of said external circuits both before and after reversing said connections.

3. A method of determining the location of etARCl-i ROOM strata in a. well in which a casing has been installed, the steps of: establishing an external flow of current between the casing and the earth; establishing an external flow of current between an electrode in the well and the earth; reversing the direction of at least one of said current flows; moving the electrode to various depths in the well; and measuring electrical changes which occur in one of said current flows, at least after the reversing of direction has occurred.

4. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of installing grounds in the earth which are electro-positive and electro-negative with respect to said casing; alternately electrically connecting said casing and an electrode movable to different positions within said well first to said electro-positive ground and then to said electro-negative ground; and measuring the electrical characteristics in at least one of said electrical connections for different positions of said electrode. 5. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of: installing grounds in the earth which are electro-positive and electro-negative with respect to said casing; moving an electrode in said well; alternately connecting electrical conductors associated with said casin and said electrode first with one of said grounds and then with the other of said grounds; and measuring the electrical characteristics in at least one of said electrical conductors.

6. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of: installing grounds in the earth which are electro-positive and electro-negative with respect to said casing; moving an electrode in said well; alternately electrically connecting said casing and said electrode first to said electro-positive ground and then to said electro-negative ground; connecting an alternating current source to said electrode and one of said grounds; and measuring the electrical characteristics of the alternating current which flows to or from said electrode.

7. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of installing grounds in the earth which are electro-positive and electro-negative with respect to said casing; moving an electrode in said well; alternately connecting electrical conductors associated with said casing and said electrode first with one of said grounds and then with the other of said grounds; connecting an alternating current source to said electrode and one of said grounds; measuring the electrical characteristics of the alternating current which flows to or from said electrode; and measuring the electrical characteristics in at least one of said electrical conductors.

8. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of: installing grounds in the earth which are electro-positive and electro-negative with respect to said casing; moving an electrode in said well; alternately connecting electrical conductors associated with said casing and said electrode first with one of said grounds and then with the other of said grounds; connecting an alternating current source to said electrode and one of said grounds; and measuring the electrical characteristics of the alternating current which flows to or from said electrode.

9. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of installing grounds in the earth which are electro-positive and electro-negative with respect to said casing; electrically connecting said casing with one of said grounds and an electrode in said well with the other of said grounds; connecting a source of alternating current potential with said electrode and one of said grounds; moving said electrode in said well; and measuring the alternating current changes to or from said electrode for different positions of said electrode.

10. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of: establishing an external flow of current between-the casing and the earth; establishing an external fiow of current between an electrode in the well and the earth; establishing an external flow of alternating current between said electrode and the earth; moving said electrode in said well; and measuring the electrical changes of said external flow of alternating current for different positions of said electrode.

11. A method of determining the location of strata in a well having a well casing installed therein which includes the steps of: establishing an external potential difference between said casing and a point in the earth; establishing an external potential difierence between an electrode in the well and a point in the earth; establishing an alternating potential difference between said electrode and the earth; moving said electrode.

in the well; and measuring the changes which occur in said alternating potential difierence for different positions of said electrode.

12. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: an external circuit between said casing and the earth; an external circuit between an electrode in said well and the earth; means for reversing the electrical potential in at least one of said electrical circuits; means for moving said electrode in said well; and means for measuring the electrical changes in at least one of said external circuits.

13. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for forming an external circuit between the casing and the earth; means for forming a second external circuit from an electrode in said well to the earth; means for reversing the connections of said external circuits to the earth; means for changing the position of said electrode in said well; and means for measuring the change of electrical characteristic in at least one of said external circuits.

14. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for establishing an external flow of current between the casing and the earth; means for establishing an external flow of current between an electrode in the well and the earth; means for reversing the direction of at least one of said current flows; means for moving the electrode to various depths in the well; and means for measuring the changes which ocour in the electrical characteristics in one of said external flows of current.

15. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: a pair of grounds adapted to be installed in the earth, one of which is electropositive, and the other of which is electro-negative with respect to said casing; means for moving anelectrode in said well; means for alternately electrically connecting said casing and said electrode first to said electro-positive ground and then to said electro-negative ground; and means for measuring the electrical characteristics between said electrode or said casing and said grounds.

16. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: a pair of grounds adapted to be installed in the earth, one of which is electropositive, and the other of which i electro-negative with respect to said casing; means for moving an electrode in said well; means for alternately connecting electrical conductors associated with said casing and said electrode first with one of said grounds and then with the other of said grounds; and means for measuring the electrical characteristics in at least one of said electrical conductors.

17. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: a pair of grounds adapted to be installed in the earth, one of which is electro-positive, and the other of which is electro-negative with respect to said casing; means for moving an electrode in said well; means for alternately electrically connecting said casing and said electrode first to said electro-positive ground and then to said electro-negative ground; means for connecting an alternating current source to said electrode and one of said grounds; and means for measuring the electrical characteristics of the alternating current which flows to or from said electrode.

18. In an apparatus for locating strata in a Well in which a casing has been installed, the combination of: a pair of grounds adapted to be installed in the earth, one of which is electropositive, and the other of which is electro-negative with respect to said casing; means for moving an electrode in said Well; means for alternately connecting electrical conductors associated with said casing and said electrode first with one of said grounds and then with the other of said grounds; means for connecting an alternating current source to said electrode and one of said grounds; means for measuring the electrical characteristics of the alternating current which flows to or from said electrode; and means for measuring the electrical characteristics in at least one of said electrical conductors.

19. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: a pair of grounds adapted to be installed in the earth, one of which is electropositive, and the other of which is electro-negative with respect to said casing; means for moving an electrode in said well; means for alternately connecting electrical conductors associated with said casing and said electrode first with one of said grounds and then with the other of said grounds; means for connecting an alternating current source to said electrode and one of said grounds; and means for measuring the electrical characteristics of the alternating current which flows to or from said electrode.

20. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: a pair of grounds adapted to be installed in the earth, one of which is electropositive, and the other of which is electro-negative with respect to said casing; means for electrically connecting said casing with one of said grounds and an electrode in said well with the other of said grounds; means for connecting an alternating source of alternating current electrical characteristics with said electrode and one of said grounds; means for moving said electrode in said well; and means for measuring the alternating current electrical characteristics to or from said electrode.

21. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for establishing an external flow of current between the casing and the earth; means for establishing an external flow of current between an electrode in the well and the earth; means for establishing an external flow of alternating current between said electrode and the earth; means for moving said electrode in said well; and means for measuring the electrical changes in said external flow of alternating current.

22. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for establishing an external flow of current between the casing and the earth; means for establishing an external flow of current between an electrode in the well and the earth; means for establishing alternating current external of the earth between said electrode and the earth; means for moving said electrode in said well; and means for measuring the changes which occur in said alternating current.

23. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for establishing an external mach KUUM potential difference between said casing and a point in the earth; means for establishing an external potential difference between an electrode in the well and a point in the earth; means for establishing an alternating potential diflerence between said electrode and the earth; means for moving said electrode in the well; and means for measuring the changes which occur in said alternating potential difference.

24. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for establishing an external flow of current between said casing and a point in the earth; means for establishing an external flow of current between an'electrode in the well and a point in the earth; means for establishing an alternating potential difference between said electrode and the earth; means for moving said electrode in the well; and means for measuring the changes which occur in said alternating potential difference.

25. In an apparatus for locating strata in a well in which a casing has been installed, the combination of: means for establishing an external flow of current between the casing and the earth; means for establishing an external flow of alternating current between an electrode in the well and the earth; means for moving said electrode in said well; and means for measuring the electrical changes of said external flow of alternating current.

GEORGE HENRY ENNIS. 

